Riser composition and a method of using the same



United States Patent C) RISER COMPOSITION AND A METHOD OF USING THE SAME Harry Baldwin Kinnear, Columbus, Ohio, assignor, by mesne assignments, to Chromium Mining and smelting Corporation, Limited, Sault Ste. Marie,0ntario,..Can-. ada, a corporation of Ontario No Drawing. Application October 5,1953, Serial No. 384,334

2 Claims. (Cl. 22'21'5)- This invention relates to a riser compositionand'toa method of using the same More particularly, the/ invention relates toa riser composition for maintaining the risers of copper-base castings fluid for a. periodrof time beyond which such risers would normally solidify whereby to substantially prevent pipe and to provide even shrinkage of the riser.

Heretofore, riser compositions for copper-base-rcastings such as brass or bronze castings have generally included copper oxide, a reducing agent for the copper oxide and a fluxing material. These. known riser compositions are exothermic and are ignited in contactwith the molten riser of a copper-base casting to. react with formationof metallic copper and a supernatant slag and with theevolu= tion of. considerable. heat. The. known exothermic. com? positions provide a layer of molten copper incontact with the top of the riser and do not contaminate the material of the. riser with undesired metallic constituents such as iron. While such riser compositions aregenerally satisfactory, they are expensive.

An object of the present invention is to provide. ariser composition for copper-base alloy castings that will'maintain the riser fluid for an extended .period of. time without contamination of the .riser. The compositions of 'the present invention do' not necessarily include .copper. oxide as. an ingredient and are composed of relatively inexpensive ingredients.

Another object of the invention is to provide a relatively inexpensive riser composition for copper-base castings that includes iron and .yet does not contaminate therisers withany substantial quantity of Another object is to provide a process for maintaining.

iron-containing exothermic "composition that burns to form a slag containing substantially no'metallic iron or only very small amountsof'metallic iron as inclusions in the slag. Where metallic "iron inclusions .arepresent: in the slag theyare. largely out of contactwith me, copper alloy riser and hence do' not'add to the riser anysub'stanrial-quantity of iron. It is important that the .risers .do not pick up iron becausethey are removedifrom the cast: ings after solidification and are remelted withadditional casting metal for reuse. Any substantial iron pick-up in the risers, gates or hot tops would result in an undesirably high iron analysis of casting metal in which such risers and the like are reused.

The-exothermicrisercompositions-of-the-present--inven agent, an oxidizing agentand-a fluxing-or-slag-formingin--- gradient. Preferably ferrosilicon having; a high :silicon content is used as the reducing agent,"althoughjotherre ducing agentssuchtasr calcium .silicide. maybe used. A silicona content of or more is preferred.

Preferably, sodium-nitrate: is .used as the oxidizing {agent although; other oxidizing agents such as potassiuminitrate an alkali metal chlorate, an alkali metal perchlorate or manganese dioxide may be used. The oxidiiihg agent normallyjsa solid material at ordinary room temperatures.

The .sla'g-fo'rmingingredient preferably is mill scale whichis substantially Fe304. Other fluxing or slag-form? ingingredientssuch as other-oxides of iron or alumina may also be employed to advantage either singly or in combination. The.- fluxing. agent may. be. ferric oxide, F5205.

Theingredientsofthe composition are so chosen and soproportioned. as toliberate upon. combustion a. large amount. of..heat .that is. sufficient to. form .a fluid slag that maintains the riserfluid for a substantialperiodof. time. The composition of the slag formed is.more or less a new tral' sodium-iron silicate.

Suflicient oxidizing agent-is incorporated in the compositionto .oxidizeallof the siliconofthe ferrosiliconto SiOa. If:..insuflicient oxidizing agent is. used, the silicon of .the...fe'rrosilicon may reduce someofthefluxingma terial .to..yield.= metallic iron. which must be kept at a minirnum.=in...the slag.

Wheresodiumnitrateis used astheoxidizingagent, the reaction is believed :to. proceed-substantially.inaccord-ance with I the. following equation:

The stoichiometric ratio of sodiiimnitrate to siliconin accordance. with this reaction is about 2.45 parts ofsodium nitrate. by weightto each part byweight of. silicon. However, theratio ofsodium nitrate to silicon maybe varied withinreasonable limits and amounts ranging from abbut 2parts of'sodium. nitrate .to 3 /z' partsiof sodium III? trate' for each part of silicon can be used. Preferably, from 24 parts of sodium nitrate. for each part .of silicon are employed. Where mill scale is used Lasthe fluxingmaterial, suflicient mill scale is incorporated to.-form aneutral iron silicate slagwith that part ofv thesilica producedby the'exothermi-c reaction that is not. associated. with the metalbxide residue of the-oxidizingnagent in aneutral alkali meta-l. silicate.

As mentioned hereinbefore the. componentstof. the. exothermic mixture are preferably so .chosen that .the 're- 'sulti'ng sla'g will be a substantially neutral one. The metal oxide fraction of theoxidizing.agententers. thev slag as agneutral silicate. For example, where sodiumnitrateis the oxidizer, two. molecules offNazO combine with...one molecule .of' Si'Oz to provide neutral sodium. silicate .of the formula Na4SiO4. Referring to Equation 1%.. l..her.einbefo're it will be seen that for each twomoleculesof Nazo P .oduced,five molecules of SiOz are. concurrently yielded. Since the two molecules of Na20 combinewith one molecule of SiOz, itwillbe seen that four molecules ofSiOaare in excess of the amount requiredfor. a neutral slag., A fluxing materialfis added to the ingredients of the exothermic reaction mixture to satisfy the requirements offtheexcesssilica to form. a neutral'slag; Thus,. .where mill'scale is used as a fluxing agent, four molecules of FesO4 in the form of mill scale are included for each five molecules of silicon and four molecules of sodium nitrate in the reaction mixture. The four molecules of FesOr combine with the four molecules excess of SiOz resulting from the exothermic reaction to provide a neutralz-irorr silicate slag of the composition FeaSiOs. The reaction thus may be summarized in the following equation:

Equation No. 2

. I The amount of fluxing agent may vary somewhat from V that'required to yield a neutral silicate slag. The resulting slag may..be either acid or basic within reasonable limits.

to eight molecules of Fea04 may be incorporated in the reaction mixture. The employment of other fiuxing agents such as alumina is governed by similar principles. In accordance with Equation No. 2, each part by weight of silicon requires 2.45 parts by weight of' sodium nitrate 5 and 6.6 parts by weight of FeaOs. For each part by. weight of silicon the sodium nittrate may fall within the range of 2V to 3% parts by weight and the F6304 may fall within the range 3 to 12 parts by weight.

Riser compositions in accordance withthe invention are in the form of an intimate mixture of finely divided materials. The compositions may be employed as mixtures of powered ingredients or the powdered ingredients preferably are formed into agglomerates or briquettes. J If agglomerates are desired, itis beneficial to employa 15 binder. The oxidizing agent itself may form the binder or an auxiliary binding material may be added to the powdered mixture and the mixture thereafter formed into agglomerates. Binders such as molasses water, waste sulfite liquor or inorganic binders such as sodium silicatemay be used. Conventional methods are employed toform agglomerates such as pressing or rolling the powderiinto balls. Agglomerates approximating spheres having diameters from /1" to /2" are especially suitable but the size and shapeof the agglomerates may vary.

In use, the riser compositions of the invention are placed upon the top of a molten riser of a copper-base alloy casting immediately after pouring and while the riser is still fluid. The heat of the molten metal in the riser ignites the composition of the invention which burns with the evolution of large amounts of heat. The slag formed by the self-contained combustion of the material is fluid and remains hot for a sufiiciently long time to insure proper feeding of the casting from the riser during solidification of the casting. Any metallic iron that remains fromthe ferrosilicon of the composition tends to agglomerate into minute shot-like particles thatremain suspended in the slag and do not come in contact with the metal of the riser. It is highly desirable and very imorder that residual iron be kept at a minimum. Ferrosilicon having at least 90% silicon and preferably having 95% silicon is preferred. Ferrosilicon metal of 98% or greater purity may be used in whole or in part.

After the copper-base casting has solidified, the frozen slag resulting from treatment of the riser in accordance with the present invention is readily and cleanly broken away from the riser and discarded. The riserjs separated from the casting in the usual manner. The risers treated by the compositions of the-present invention show prac tically no iron pick-up and are essentially of the same composition as the original copper-base alloy. These risers are clean and can be re-melted for further casting operations.

The following table illustrates the iron pick-up in risers per application of a typical riser composition (Mill scale parts, sodium nitrate 24 parts, and ferrosilicon% Si-11 parts by weight), the maximum iron build up where each melt subsequent to the first contains 40% of risers from a previous cast to which the riser composition of theinvention is applied and a comparison of these values with ASTM specifications for maximum iron content.

TABLE I Iron Pick Maximum Maximum Up per Iron Build Iron Con- Appllea- Up with 40% tent; A. 8. Type oi Copper-Base Alloy tion of of Riser in T. M. Spec- Riser Com- Each Melt, ificatlons, position, percent percent;

percent (1) Leaded Red Brass: 85 Cu,

5 Sn, 5 Pb, 5 Zn 0. 01-0. 03 0 017-005 0.30 (2) Yellow Brass: 60 Cu, 40 Zn, 0. 06-0. 15 0 10 0. 25 0. 60-0. 75 (3) Leaded Tin Bronze: 87 Cu,

8 S11, 1 P 4 Zn 0.01-0.05 0 017-0. 084 0.16-0.25 (4) Manganese Bronze (High I Strength Yellow Brass)-.- 0.11 0.18 2.0 3. 0 (5) Aluminum Bronze 0.03 0.05 2 5 5.0

From the foregoing table it is seen that where riser compositions of the present invention are employed the iron pick-up in risers per application of the riser composition'of the invention is negligible and the maximum iron build up where 40% of risers are reused in subsequent melts is far below maximum ASTM specifications.

The invention will be illustrated and described with greater particularity in the following detailed examples.

Example 1 mixture is added 31 lbs. of molasses water containing 8 portant that the ferrosilicon be of a high silicon grade in 40 lbs. of black strap molasses and 23 lbs. of water as a binder. The mixture is tumbled in a rotary mixer to form nodules ranging in size from A" to /6" in diameter. As the nodules are formed they are removed from the tumbling mixture. The green nodules are dried in an oven at C. until the moisture content is less than about, 1%. The nodules as dried are ready for use in treating risers of copper-base castings.

Suflicient of the riser compound is employed to provide from /2 to of'slag on the riser. The mixture is ignit'ed on the top'of a riser of a freshly poured yellow brass casting. The mixture ignites readily from the heat of the riser and burns rapidly. The slag produced by the riser composition is broken and examined after freezing and only a few tiny beads of metal are found dispersed in the slag. The brass casting is sound and the riser is flat on top and has no pipe.

, Table II hereinafter shows the composition of additional riser mixtures in accordance with the invention. The procedures for making and using the mixtures are similar to those described in Example I.

Each of the mixtures of Table II ignites readily and burns rapidly. Only a few tiny beads of metal are found in the slags resulting from combustion of the mixes.

I claim:

1. An exothermic riser composition for providing a hot top on the risers of copper-containing castings to prevent pipe consisting essentially of ferrosilicon containing more than 90% silicon, sodium nitrate and mill scale in the substantial molecular ratio of 5 molecules of silicon to 4 molecules of sodium nitrate to 4 molecules of FesOa.

2. A process for maintaining the risers of copper-containing castings fluid to prevent pipe which comprises igniting in contact with the top of a molten riser of a copper-containing casting an exothermic riser composition consisting essentially of an intimate mixture of finely divided ferrosilicon containing more than about 90% silicon,

sodium nitrate and mill scale in the substantial molecular ratio of 5 molecules of silicon to 4 molecules of sodium nitrate to 4 molecules of FesO-r.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Metallurgy of Copper, by Newton-Wilson (1942 edition), pages 120 and 121 relied on. 

1. A PROCESS FOR MAINTAINING THE RISERS OF COPPER-CONTAINING CASTINGS FLUID TO PREVENT PIPE WHICH COMPRISES IGNITING IN CONTACT WITH THE TOP OF A LOLTEN RISER OF A COPPER-CONTAINING CASTING AN EXOTHERMIC RISER COMPOSITION CONSISTING ESSENTIALLY OF AN INITMATE MIXTURE OF FINELY DIVIDED FERROSILICON CONTAINING MORE THAN ABOUT 90% SILICON, SODIUM NITRATE AND MILL SCALE IN THE SUBSTANTIAL MOLECULAR RATIO OF 5 MOLECULES OF SILICON TO 4 MOLECULES OF SODIUM NITRATE TO 4 MOLECULES OF FE3O4. 